The present invention relates to a method of forming a pattern of a photomask used in the manufacture of a semiconductor device, a liquid crystal substrate and the like, and a method of forming a semiconductor device using the photomask.
In the conventional method of forming a pattern, for example a metal film pattern, on a substrate, a metal film is deposited on the entire surface of a substrate, followed by coating the entire surface of the metal film with a photoresist. Then, the photoresist is selectively exposed to light by using a photomask, followed by developing the patterned photoresist so as to form a resist film pattern. Thereafter, the metal film is selectively exposed to light by using the resist film pattern as a mask, followed by developing the exposed metal film so as to form a metal film pattern. This is also the case with the manufacturing method of a semiconductor device. Specifically, a metal film, i.e. a conductive film, is deposited on the entire surface of a semiconductor substrate, followed by coating the entire surface of the conductive film with a photoresist. Then, the photoresist is selectively exposed to light by using a mask, followed by developing the patterned photoresist so as to form a resist film pattern. Thereafter, the conductive film is subjected to etching by using the resist film pattern as a mask, so as to form a wiring or a gate electrode.
FIGS. 10A to 10C are cross sectional views collectively showing a conventional method of forming a wiring pattern or a gate electrode on a semiconductor substrate by using a photomask. In the first step, a light shielding film 101 consisting of chromium (Cr) is formed on the entire main surface of a transparent substrate 100 such as a glass substrate. Then, the entire surface of the light shielding film 101 is coated with a positive or negative resist 102, as shown in FIG. 10A. Then, a predetermined pattern is depicted on the resist layer 102 by irradiating the resist layer 102 with a light or an electron beam in a predetermined pattern, followed by developing the depicted pattern so as to form a resist film pattern 102, as shown in FIG. 10B. Further, the light shielding film 101 is selectively etched with the resist film pattern 102 used as a mask so as to form a light shielding film pattern 101. Then, the resist film pattern 102 is removed. As a result, a photomask consisting of the transparent substrate 100 and the light shielding film pattern 101 is formed, as shown in FIG. 10C.
The photomask is constructed in conformity with a circuit pattern of, for example, a wiring and a gate formed on a semiconductor substrate. To be more specific, the photomask comprises a transparent substrate such as a glass substrate, and light shielding film patterns e.g. chromium film patterns, formed on the main surface of the transparent substrate. The light shielding film patterns may be arranged collectively or at a high density in some region so as to form a collective or dense arrangement pattern and a single light shielding film pattern is independently formed in another region so as to form an independent or isolated arrangement pattern. The arrangement patterns are determined by the construction of a circuit formed on a semiconductor substrate. The main surface of the semiconductor substrate is classified into region A in which the light shielding film pattern or patterns are formed and region B in which the light shielding film pattern is not formed. In a region A in which the light shielding film patterns are collectively provided includes portions in which the light shielding film patterns are formed, portion or portions in which the light shielding film pattern is not formed, i.e., portion or portions located between the adjacent light shielding film patterns, and portions located between the outermost light shielding film pattern and region B. In another region A in which the single light shielding film pattern is independently provided includes a portion in which the light shielding film pattern is formed, and portions between the light shielding film pattern and region B. On the other hand, region B includes a portion in which nothing is formed on the main surface of the substrate.
In forming above mentioned photomask having collectively arranged light shielding film patterns and an independently arranged light shielding film pattern present together on the substrate, a difference in size is generated between the collectively arranged light shielding film patterns and the independently arranged light shielding film pattern. As a result, it is difficult to form a photomask having a uniform size of the collectively arranged light shielding film patterns and the independently arranged light shielding film pattern. Thus, if a resist film pattern is depicted by light or an electron beam in forming a mask, it is difficult to depict the pattern as designed because of the influence of the proximity effect. Further, in the step of developing the resist film, a size difference is generated depending on, for example, the regions developed. Also, in the step of etching the light shielding film by using the resist film as a mask, if a region, in which the etching amount is large in the etching step of the light shielding film, and another region, in which the etching amount is small, are present together, a size difference is also generated. As a result, it is difficult to form a wiring pattern and a gate pattern as designed on the semiconductor substrate. How to eliminate these difficulties is a serious problem to be solved in forming a photomask.